The present invention relates to well drilling technology. More particularly, the present invention relates to a method and apparatus for controlling the ascent and descent of vertical pipe or other tubular members passing through a pipe or casing slip into a well borehole.
It is well known in the oil well drilling art that pipe or casing slip assemblies are utilized in oil field operations for drilling, setting casing, or placing or removing any tubular member from a well bore. An excellent explanation of the function and operation of drill pipe slip assemblies is provided in U.S. Pat. No. 6,471,439, which is incorporated herein by reference for all purposes.
One of the most significant problems encountered in setting slips is maintaining control of the descent of the pipe into the slip and the slip into the slip bowl. The extensive lengths of piping in a drill string may result in considerable weight having to be controlled by the rig operator's braking procedures. Dropping the weight too quickly may result in damage to the pipe wall leading to fatigue of the pipe or breaking of the slip dies. If a pipe section fails the entire length of the drill string below the failure may be lost. Attempts to pull stuck drill strings from the well bore often puts site personnel at considerable safety risk. The draw works (block and tackle arrangement) may snap or the derrick rigging itself may collapse. These problems are associated with the pulling or supporting of the drill string from above the rig platform and, more particularly, having the pulling or supporting force coming from above the top surface of the slip. Casing jacks have been used in the past to pull old casing from the well bore. However, these are set up after the well is drilled. With the present invention the float system may be in place before the drilling starts.
The present invention provides a number of embodiments which push or support the drill string from beneath rather than pulling from above. The same method and apparatus allows for the string to be cushioned, controlled, or dampened in its descent thereby reducing pipe or casing wall failures. Thus, the present invention further reduces the likelihood of broken slip teeth (dies) and crimping and fatiguing of the pipe wall which results in pipe failure.